Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Wakefield Virginia
151 am EDT Sat Jul 22 2017
hot and humid conditions will continue over the region through
Sunday. A weakening cold front will gradually push across the
area late Sunday through Monday, with temperatures cooling down
to near normal levels Monday through Thursday.
Near term /through today/...
weak sfc/Lee trough in place across the local area this evening,
with west-northwest flow prevailing aloft around the base of an upper
level trough centered over eastern Canada. Very warm and humid
as of 9 PM. Temperatures are still mainly in the 80s, with
dewpoints ranging through the 70s to around 80. Earlier
convection dissipated very quickly as it entered the northwest corner
of the cwa, and isolated convection over NE NC has dissipated as
well with mainly dry conditions expected through midnight. Some
isolated convection (20% chc) is possible late from the nrn
neck to the Maryland ern shore.
Remaining very warm/humid overnight with lows mainly 75 to 80
f. Not as hot most areas for Sat, due to potential for more
clouds and as core of 850 mb heat shifts a bit S. However, with
slightly higher dew pts than Fri expect most of the area to
reach heat advisory criteria Sat aftn even with highs on avg
only in the mid 90s. As airmass destabilizes more by Sat
aftn/early evening, and as heights aloft drop, convection
developing from the northwest will be more likely to hold together for
at least 30-50% pops across most areas (20% NE nc) from late Sat
aftn through Sat night. Deep layer shear will be higher as the
upper trough sharpens a bit and 500 mb to 700 mb flow increases. Most of
the County Warning Area is in a marginal risk for severe wx, with a slight risk
for the far N/NE. Wind will be the primary threat with large
hail also possible.
Short term /tonight through Monday/...
lows mainly in the mid to upper 70s Sat night, and continued
hot and humid with additional heat headlines likely needed for
some of the region on sun. Highs mainly in the mid to upper 90s
Sunday. Slight risk in place for most of the cwa, but more
uncertainty exists depending on how long convective debris from
Sat night hangs around and potentially keeps more clouds around.
Cold front slated to pass through while weakening late Sun night
through Mon. Will maintain chc pops all zones Sun night, and
favor highest pops Mon across the S with 20% pops for the north.
Slightly less humid Monday, especially north. Highs Mon 90 to 95 f.
Long term /Monday night through Friday/...
cold front progged to push offshore Tuesday morning as the upper
trough slides over the northeast into the Canadian Maritimes.
Deepest moisture pushes offshore late Monday night, but will keep
mention of slight chance to chance pops near the coast. Southern
portion of the cold front expected to stall over the Carolinas
Tuesday as a baggy trough locates over the southeast. Combination of
weak energy in the upper flow and a moist air mass near the
boundary, will keep mention of slight chance to chance pops across
the far southeast local area Tuesday afternoon. Otherwise, cooler
Tuesday with a light north to northeast wind. Highs generally in the
upper 80's to around 90 (near seasonable norms). High pressure at
the surface and aloft slides north of the region Tuesday night into
Wednesday as another trough tracks across Ontario. Meanwhile, a
broad upper ridge over the Southern Plains expands eastward, but the
baggy trough remains over the southeast. Best chances for measurable
precip expected to be south of the region Wednesday, but will carry
slight chance to low end chance pops across the southern portions of
the forecast area. Highs Wednesday generally in the mid 80's.
Another trough tracks into the Great Lakes and northeast Wednesday
night and Thursday, pushing another weakening cold front into the
mid-Atlantic region Thursday afternoon. Will need to watch for
upstream convection Wednesday night in northwest flow aloft, so have
added chance pops for the Maryland Eastern Shore. With the boundary
and cyclonic flow over the region Thursday, have chance pops for
diurnally driven showers and thunderstorms. Highs Thursday generally
in the upper 80's to low 90's. Medium range guidance depicts
additional energy digging down the backside of the upper trough
Friday, with a wave of low pressure progged to develop along the mid-
Atlantic front. Timing and spatial differences at that timeframe of
the forecast cause a great deal of uncertainty, so have only
mentioned 20-40% pops at this time. Highs back around seasonal
norms, in the upper 80's to low 90's.
Aviation /06z Saturday through Wednesday/...
VFR conditions at area terminals this morning, with VFR
conditions to prevail through the 06z taf period. High pressure
will continue to prevail off the southeast coast tonight into
Saturday, with a lingering trough to the Lee of the central
Appalachians. This will result in primarily light SW flow at
~5-10kt. Sct to occasionally bkn mid and high clouds overnight.
Mainly dry conditions are expected tonight with a minimal chc
of showers/tstms at sby through 10z (sct showers now crossing
from north of an esn to Ged line at issuance time).
Sct cu with bases ~5-6kft develop by late morning ahead of a
weak upper level system. This feature should trigger isolated to
scattered showers/tstms late this afternoon and evening. The
best chc (30-50%) is from ric-sby and north, with a 20-30% chc
for phf/orf/ecg. Have included vicinity thunder wording at sby
and ric, but have held out elsewhere for now.
Outlook: another period of late aftn/evening showers/tstms
expected Sunday, shifting south into south central Virginia and NC
for Monday. VFR should dominate through this period, with
periods of periods of sub-VFR possible in heavier showers/tsra.
A weak cold front pushes through the area Tuesday with high
pressure building north of the region Wednesday.
latest surface analysis depicts high pressure over the
western Atlantic with a trough of low pressure over central
Virginia. Obs indicate a light south to southeast winds at or below
10 knots. Waves are generally 1 foot and seas 2 feet. Diurnal
increase in the low level winds expected again tonight over the Low
Bay and southern coastal waters. Hi-res guidance depicts winds
around 15 knots, with an occasional gust of 18 knots, mainly
centered a few hours either side of 11pm (03z). Conditions expected
to remain sub-sca. Wave kick up to 2 feet in the Lower Bay and seas
2-3 feet. Stagnant surface pattern persists through the weekend.
Winds generally southwest at or below 15 knots, but near Small Craft Advisory
conditions possible late each day into the overnight period. Seas
generally 2-3 feet (upwards of 4 feet overnight) with waves of 1-2
A weakening cold front approaches the region late Monday, dropping
across the region Monday night into Tuesday morning. Flow backs to
the northwest to north Tuesday at or below 10-15 knots. High
pressure builds across the northeast into Wednesday, resulting in
onshore flow Wednesday. Another weakening cold front approaches the
region Wednesday night and Thursday, stalling over the region into
heat wave is expected to continue through Sunday. The 2nd half
of July is climatologically the hottest few weeks of the year,
so we still may not set any daily records at our main climate
sites. For reference, record highs for Saturday and Sunday are
* date: sat(7/22) sun(7/23)
* ric: 103/1952 103/1952
* orf: 102/2011 103/2011
* sby: 104/1930 103/2011
* ecg: 104/1952 104/1952
Maryland...heat advisory from 10 am this morning to 8 PM EDT this evening
NC...heat advisory from 10 am this morning to 8 PM EDT this evening
Virginia...heat advisory from 10 am this morning to 8 PM EDT this evening